I. Field of the Invention
The invention relates to a process and to an apparatus for the treatment of untreated water; for example, surface water, waste water, sewage and the like.
II. Description of the Prior Art
The treatment serves to remove substances causing turbidity contained in the untreated water in order to obtain clean water. This is brought about by adding a flocculating agent to the untreated water in order to form the substances causing turbidity into flakes which are separated by sedimentation. For this purpose, the untreated water mixed with the flocculating agent is passed through sedimentation tanks in which flake formation occurs and in which the flakes formed settle through sinking, while the flake-free untreated water rises upwards on flowing through the sedimentation tank and is removed from the water surface as clean water. On flowing through the sedimentation tank, the untreated water mixed with the flocculating agent must spend an adequate time in the tank in order to permit flake formation, while in the sedimentation tank there must be a vertically upwardly directed flow which must be smaller than the sinking speed of the flakes to be sedimented, so that they can be deposited on the tank bottom as sludge and the clean water can be drawn off from the water surface of the tank. The shapes and construction of the sedimentation tanks are determined by these requirements.
Various sedimentation tank constructions are known. In one version, which is in the form of a rectangular tank, the untreated water mixed with the flocculating agent is fed into the lower tank area at a narrow side and after flowing through the tank, the clean water is removed from the water surface at the opposite narrow side, while the sludge on the tank bottom resulting from the deposited flakes is intermittently removed by scraping or raking. In addition, cylindrical sedimentation tanks are known in which the untreated water is supplied from below into a chamber positioned centrally within the tank and which is equipped with agitating blades. The untreated water is removed below the water level from the chamber in a downwards direction into the tank in which flake formation and deposition occur, while the rising clean water is collected and removed by means of an overflow intersecting the water surface.
To ensure an optimum operation of the sedimentation tank, it must be ensured that a uniform throughflow is obtained which covers the entire cross-section of the tank, where they are only limited vertical flows permitting the sinking of the flakes. The loading capacity and therefore the efficiency of the complete sedimentation tank is reduced if even at a single point there is an increased upward movement. This is also the case if there are areas within the tank which are not covered by the through-flow, so that the entire available volume can not be utilized for sedimentation purposes.
In order to satisfy these requirements, all known sedimentation tanks require complicated and costly units for guiding the supplied water, without it being possible with absolute reliability to bring about, on the one hand, the necessary uniform flow over the entire tank cross-section and, on the other hand, a uniform upwardly directed flow with the necessary low speed, so that, despite the necessary expenditure, the capacity of known sedimentation tanks must always be made greater as a result of the irregularities which occur than would be necessary with completely satisfactory flow conditions.